Can anyone give me a quick how-to on removing the diffuser? I have a CF one on the way but it sounds like its a little more difficult than the 135i...

I know it well

There are 4 plastic rivets (2 each side) which are a single use only. Just drill out the centre if each, then the OE diffuser can be pulled out starting one side to the other. The clips/tabs are quite secure though and it is a hard pop in/out.

Not sure yet... Asked Stu to find me one... The discussion went something like this:

ME: "All the diffusers out there suck. The brand name ones are ridiculously priced and I don't like most of them. The eBay ones are all questionable quality and they're stupidly priced too. Can you find me a decent one at a decent price?"

STU: "Sure."

A day or so later he told me he'd found and ordered one. That was a month or so ago. (They had to fabricate it after he ordered it.)

It arrived at Advan today and hopefully it's already on its way to me..